Emailing Invoices

When we create monthly invoices (approx 3k each month), we mark them where they don't automatically email invoices out. We do this so that we can apply any open credits to invoices. We have been running a script to email invoices to main and CC emails. This is now causing another script to trigger on each invoice (it is a script that makes our pricing and discounts that we cannot turn off). This is causing invoices to get emailed out over roughly 72 hours. This seems like it is taking too long.

What are the normal ways that you use to email mass invoices after they are created? Is it via an import? Different settings? Just trying to see what other options we have to try out.